Single pump hydrostatic transmission control and supply system

ABSTRACT

A system for supplying control, actuation, and other functions in a hydrostatic transmission. The supply system includes singular pump means for supplying fluid under pressure to a pressure compensated flow control valve which functions to supply a constant volumetric rate of fluid flow to a modulatable speed control valve. The modulatable speed control valve creates a pressure differential thereacross which differential is communicated to direction and speed control cylinders for regulating pump and motor components of the hydrostatic transmission. Fluid in excess of that required for supplying the constant volumetric flow rate to the speed control valve is passed through a portion of the pressure compensated flow control valve to operate servo valves and displacement control actuators in the transmission. The pressure of such excess fluid is controlled by means of a relief valve which opens to dump fluid to a drain conduit whenever the pressure of such fluid reaches a predetermined value. Additional excess fluid beyond that required for the control and actuation functions is transmitted from the relief valve to a relief and replenishing valve group for assuring an ample fluid supply for the hydrostatic transmission components. Fluid passing from the singular supply pump is transmitted through a heat compensated venturi mechanism which provides inlet and throat pressure signals, proportional to flow rate, to an underspeed safety valve means which function to open a parallel flow path to that controlled by the speed control valve at such times as the speed of the engine associated with the hydrostatic transmission drops off to cause a decrease in flow from the singular supply pump. In addition to supply fluid for the previously discussed functions, fluid supplied by the singular supply pump is also available to scavenge leakage fluid from various portions of the system by virtue of the passage thereof through a jet pump.

United States Patent [1 1 Johnson June 3,1975

[ l SINGLE PUMP HYDROSTATIC TRANSMISSION CONTROL AND SUlPLY SYSTEM [75]Inventor: Gordon W. Johnson. Peoria. ll].

[73] Assignee: Caterpillar Tractor Co., Peoria. Ill.

[22} Filed: Sept. 20, 1974 [21] Appl. No.: 507,759

Related U.S. Application Data [62] Division of Ser. No. 427.087. Dec.12. 1973.

[52] U.S. Cl. 60/488; 60/490; 60/455; 60/456; 91/444 [51] Int. Cl. FlSb11/02 [58] Field of Search 9l/418, 444; 60/473, 487, 60/488, 490

[56] References Cited UNITED STATES PATENTS 3,142,962 8/l964 Lohbaucr60/427 X 3.477.225 ll/l969 Cryder et al 60/427 X Primary Examiner-EdgarW. Geoghegan Attorney, Agent, or FirmPhillips. Moore, Weissenberger,Lempio & Strabala 57 ABSTRACT A system for supplying control. actuation,and other functions in a hydrostatic transmission. The supply systemincludes singular pump means for supplying fluid under pressure to apressure compensated flow control valve which functions to supply aconstant volumetric rate of fluid flow to a modulatable speed controlvalve. The modulatable speed control valve creates a pressuredifferential thereacross which differential is communicated to directionand speed control cylinders for regulating pump and motor components ofthe hydrostatic transmission. Fluid in excess of that required forsupplying the constant volumetric flow rate to the speed control valveis passed through a portion of the pressure compensated flow controlvalve to operate servo valves and displacement control actuators in thetransmission. The pressure of such excess fluid is controlled by meansof a relief valve which opens to dump fluid to a drain conduit wheneverthe pressure of such fluid reaches a predetermined value. Additionalexcess fluid beyond that required for the control and actuationfunctions is transmitted from the relief valve to a relief andreplenishing valve group for assuring an ample fluid supply for thehydrostatic transmission components. Fluid passing from the singularsupply pump is transmitted through a heat compensated venturi mechanismwhich provides inlet and throat pressure signals, proportional to flowrate, to an underspeed safety valve means which function to open aparallel flow path to that controlled by the speed control valve at suchtimes as the speed of the engine associated with the hydrostatictransmission drops off to cause a decrease in flow from the singularsupply pump. In addition to supply fluid for the previously discussedfunctions, fluid supplied by the singular supply pump is also availableto scavenge leakage fluid from various portions of the system by virtueof the passage thereof through a jet pump.

4 Claims, 1 Drawing Figure SINGLE PUMP HYDROSTATIC TRANSMISSION CONTROLAND SUPPLY SYSTEM This is a division, of Ser. No. 427,087.f1led Dec. 12,1973.

BACKGROUND OF THE INVENTION Heavy earth moving vehicles frequently usehydrostatic transmissions because of their adaptability to varying loadapplications and because they afford an infinitely variable ratiobetween the speed of the vehicle engine and the ground speed of thevehicle. The most frequently utilized hydrostatic transmissions employ apump and motor, both of which have variable displacementcharacteristics.

Such transmissions require an especially effective and precise controlsystem since relative changes in the displacement of the pump and motormust be properly sequenced for efficient operation of the transmissionand for providing a desirable torque ratio for the system. For anexample of such a control system for a hydrostatic transmission,reference may be had to US. Pat. application Ser. No. 222,041, filed onJan. 31, [972 now US. Pat. No. 3,771,310 by John R. Cryder, et al,entitled Hydrostatic Drive Control System. The system disclosed in saidapplication includes a so-called positive pressure speed control"arrangement and is assigned to the Assignee of the present invention.

Because of the precise requirements of such hydrostatic transmissioncontrol systems, prior art systems have often been complicated andexpensive by virtue of the multiplicity of special valves and othercomponents required. Some prior art systems included separateindependent supply pumps for supplying fluid for various functionsincluding speed control, relief and replenishing, and operation ofdisplacement control actuators. Despite the additional hardware in suchmultiple pump arrangements, the results have often been less thanoptimum owing chiefly to the need for additional horsepower which mustbe diverted from tractive effort for the operation of the arrangementand to the often insufficiently sensitive response thereof to systemdemands. Some additional examples of prior art control systems areprovided by US. Pat. Nos. 3,187,509; 3,212,263; 3,236,049; 3,238,724;and 3,247,669.

SUMMARY AND OBJECTS OF THE INVENTION The instant invention provides animproved control and actuation system for a hydrostatic transmission.The invention includes a single supply pump for supplying fluid to apressure compensated flow control valve which valve provides a constantvolumetric flow rate for a manually operated differential pressure-typespeed control valve for controlling the speed and direction of thecomponents of the hydrostatic transmission. The system also includesunderspeed valve means and a heat compensated, speed-sensing venturimechanism for the operation thereofv The singular supply pump alsosupplies fluid for actuating the displacement control actuators of apump and motor of the transmission and for a relief and replenishingsystem therefor. Fluid supplied by the singular supply pump in excess ofthat required for speed control, actuation, and relief and replenishingfunctions, is utilized to drive a jet pump which scavenges fluid leakagefrom various areas of the vehicle to which the transmission is adapted,such as the gear case.

One of the objects of the present invention is to provide a control andsupply system for a vehicle hydrostatic transmission which requires thediversion of relatively little power from tractive effort of thevehicle.

Another object of the present invention is to provide a control andsupply system with superior speed control characteristics owing to theuse of a differential pressure speed control valve operatively suppliedby pressure compensated flow control valve which supplies a constantvolumetric fluid flow rate regardless of vehicle engine speed.

A still further object of the present invention is to provide a singlepump supply system which supplies fluid for speed control of ahydrostatic transmission while also supplying driving fluid for a jetpump usuable for scavaging leakage fluid.

Other objects and advantages of the present invention will becomeapparent from the following description and drawing.

BRIEF DESCRIPTION OF THE DRAWING The sole FIGURE in the drawing is aschematic representation of the essential components of the instantcontrol and supply system.

DETAILED DESCRIPTION With reference to the drawing, the components andoperation of the instant single pump control and supply system may beappreciated. A hydrostatic transmission which is controlled by theinstant system is comprised of a variable displacement reversible pump102 and a variable speed motor 98 intercommunicated by fluidcommunication means 103. The displacements of the pump and motor areconventionally controlled by conventional displacement actuators 112 and114 which are, in turn, controlled by displacement servo valves 108 and110, respectively, which regulate the flow of fuid to the displacementactuators. The servo valves are, in turn, regulated respectively by adirection and displacement control cylinder and a-speed control cylinder96 mechanically linked to the servo valves.

The transmission is also equipped with a standard relief andreplenishing valve group suitably communicated to the instant controlsystem by fluid communication means 118, 200, and 124. As will becomeapparent from the following discussion, fluid for the speed anddirection control elements of the hydrostatic transmission as well asfor the displacement actuators and relief and replenishing system willbe supplied by the single pump control and supply arrangement of theinstant invention.

The instant control and supply system includes a fluid pump 10 whichdraws fluid from a low pressure reservoir 11 through a conduit 12 andsupplies fluid through a conduit 13 to a heat compensated venturimechanism shown generally at 16. The size and capacity of pump 10 isdetermined by calculating the amount of fluid to properly cool thesystem and adding to that the anticipated fluid leakage from the system.Pilot signals from the inlet and throat portions of the venturi areprovided to an underspeed valve 80 by means of conduits 84 and 82,respectively. The heat compensated venturi mechanism includes aconventional thermal compensator 31 which senses the temperature offluid flowing through the venturi by way of a passage 33 and, upon theattainment of a predetermined fluid temperature, shifts a spool 32rightwardly, as shown in the drawing, to permit a portion of the fluidentering the venturi through line 13 to pass through a passage 35, ports34, a passage 37, and a passage 33 to by-pass the venturi and provide aradically changed pressure signal in the system which alerts an observeras to the overheating condition.

Fluid exits from the venturi mechanism through a conduit 86 and enters apressure compensated flow control valve shown generally at 20. Thepurpose of this flow control valve is to supply a constant volumetricfluid flow rate for speed control functions. The valve includes a flowcontrolling spool 88 which has a flow restricting orifice 89 whichcommunicates an inlet chamber 91 with a spool chamber 93, as shown. Thespool also includes a plurality of radial ports 95 which communicate toa greater or lesser extent with a supply conduit 92 depending upon theposition of the valve spool 88. Another orifice 97 leads from thechamber 93 to a spring chamber 99. As may be readily appreciated fromthe drawing, the spool 88 tends to move rightwardly under the influenceof pressure in the chamber 91 and is opposed in such rightward tendencyby the spring 101 and the pressure within chamber 99. Flow through theorifice 89 creates a pressure drop in the chamber 93 which pressure dropincreases with increasing flow velocity through the orifice 89. Thegreater the pressure differential across the orifice, the further thespool 88 moves rightwardly to vary the volume of the fluid communicatingbetween the chamber 93 and the line 92. Valve spool 88 also containsradial ports in the chamber 91 to communicate excess fluid to a line 116when the spool 88 moves rightwardly to a position which enablescommunication between such ports and the line 116. A more detailedexplanation of the principal of operation of the constant volume flowrate control valve may be had with reference to U.S. Pat. No.3,142,962-to Lohbauer, of common assignment herewith.

The valve outlet conduit 92 communicates directly with a speedcontrolvalve 90, which has a modulating valve spool 71 with lands andmodulating grooves thereon, is manually actuable to create a selectivelyvariable pressure differential across the speed control valve with theupstream pressure from line 92 being directed to a branched line 94 tothe head end of the speed control cylinder 96 and to one end of thecontrol cylinder 100, as shown; Downstream pressure fluid from thedifferential speed control valve 90 is directed through a branched line104 to the rod end of the speed control cylinder 96 and to the oppositeend of the control cylinder 100 for the pump 102. A good example of adifferential speed control valve like the valve 90 is shown at 79 inU.S. Pat. No. 3,477,225 to Cryder et al, of common assignment herewith.This patent also discloses an underspeed valve 80 which functions in amanner similar to the instant underspeed valve.

A conventional manually operable direction control valve 105 is disposedacross the lines 94 and 104 to permit an operator to manually select thechamber of the control cylinder 100 to which is directed the highpressure fluid from line 94 to select the direction in which the pump102 will operate. It will be appreciated that the cylinder 100progressively varies the displacement of the pump 102 from Zero tomaximum as the piston thereof moves from the center position shown tothe extreme end positions in either direction selected by means of thevalve 105. In a typical installation, changing the direction of pump 102causes a change in the direction of the vehicle. to which the system isadapted.

The above discussion essentially completes the description of the speedand direction control functions of the instant system. The system alsosupplies fluid for operating the displacement actuators of thetransmission and for performing other functions. to be explainedhereinafter.

Fluid from the line 86 in excess of that required to supply a constantvolume of fluid to the line 92 is passed to a line 116 whichcommunicates through radial ports with the chamber 91. Some of thisexcess fluid is communicated by way of a branched line 106 to supply thepump and motor displacement servo valves 108 and 110 which, in turn,selectively supply fluid pressure to the actuators 112 and 114, aspreviously described. Also communicating with the line 116 is a reliefvalve 44 which functions to control the pressure of the fluid in thedisplacement actuator line 106. The valve 44 operates to dump excesspressure fluid to a line 128 upon movement of the spool thereinrightwardly against the bias or the spring, shown in the drawing. Itwill also be noted that fluid entering the valve 44 through the line 116is communicated by means of radial ports to the line 118 which linecommunicates directly with a relief and replenishing valve group showngenerally at 120 in the drawing. A branch line containing an orifice 122provides restricted communication between the lines 116 and 118 to avoidstarvation of the relief and the replenishing valve group duringtemporary conditions in the actuator system wherein the pressure thereinis below that necessary to open the relief valve 44 to allow flow fromthe line 116 through the radial valve ports to the line 118.

In addition to supplying fluid for speed and displacement controls, foractuation of the displacement actuators, and for the relief andreplenishing circuit of the hydrostatic transmission, the single pumpsystem of the present invention also supplies fluid for additionalpurposes. For example, some of the excess oil from the reduced pressureconduit 104 is communicated to a return line 124 which also serves toreturn excess hot fluid from the transmission to a fluid cooler 72 byway of a pressure responsive cooler bypass valve 68. Also combined withthe excess flow from the speed control valve and the flow from therelief and the replenishing group is excess fluid from the relief valve44 via the line 128.

Fluid passing through the cooler 72 or, through the pressure responsivecooler by-pass valve 68 under high pressure conditions, is transmittedto a jet pump 76. The throat of the jet pump is communicated by way of aline 77 to a source of leakage oil from the transmission. For instance,the jet pump could be used to scavenge oil leaking into the gear box 79of the vehicle to which this system is adapted.

Proximate the relief and the replenishing valve group is a double actingball check valve 200 which is interposed between the lines 118 and 124to insure that the relief and replenishing group is not starved byvirtue of communication of fluid from the line 118 to the cooler via theline 124 when the pressure in line 124 is relatively low.

It may be readily appreciated that the present system utilizes a singlepump 10 to supply all of the control and actuation functions of thehydrostatic transmission to which it is adapted. The system maintains aconstant regulated volume of fluid to a speed control system whichutilizes a pressure differential-type speed control valve so that minoroperational changes such as varying engine speed, increased pumpleakage. or the like, do not affect the speed and directional signals tothe control elements. The particular differential pressure speed controlelements utilized in the present system provide an extremely sensitivespeed control means which is particularly useful when supplied with aconstant volumetric fluid flow as is the present system.

While the invention has been described with particular reference to thepreferred embodiments, it is apparent that variations and modificationsare possible within the purview of the inventive concepts. No limitationwith respect to such variations and modifications is intended, except bythe scope of the appended claims.

I claim:

I. A supply and control system for a hydrostatic transmission including;a source of fluid under pressure, flow control valve means for providinga :onstant volumetric rate of fluid flow, first fluid communicationmeans between said source and said flow control valve means, speedcontrol valve means for regulating the flow of fluid from said constantvolumetric rate of flow control means of said hydrostatic transmission,second fluid communication means between said speed control valve meansand said flow control valve means, and third fluid communication meansbetween said speed control valve means and said speed control means ofsaid transmission.

2. The invention of claim 1 wherein said flow control valve meansinclude a first housing and a flow regulating first spool movablydisposed within said first housing, said spool having first and secondchambers therein, said first chamber communicating with said first fluidcommunication means and said second chamber communicating with saidsecond fluid communication means, first orifice means in said firstspool between said first and second chambers for creating a drop inpressure of fluid flowing from said first chamber to said second chamberfor causing movement of said first spool.

3. The invention of claim 2 wherein said source includes a fluid supplyreservoir and a singular fluid pump.

4. The invention of claim 3 wherein said hydrostatic transmissionincludes a fluid pump and a fluid motor coupled by means of fourth fluidcommunication means.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF QURRECHGNPATENT NO. 1 ,8 6, 4 DATED June 3, 1 7 lN\/ ENTOR(S) GORDON W JOHNSON Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

I A i I I fiigrted and Sealed this l Tenth Day of Au ust 1976 I Q ESEALBA A ttesr:

. RUEH C. MASON 6 Arresting Officer C. MARSHALL DANN (ammissioner ofParents and Trademarks

1. A supply and control system for a hydrostatic transmission including;a source of fluid under pressure, flow control valve means for providinga constant volumetric rate of fluid flow, first fluid communicationmeans between said source and said flow control valve means, speedcontrol valve means for regulating the flow of fluid from said constantvolumetric rate of flow provided by said flow control valve means tospeed control means of said hydrostatic transmission, second fluidcommunication means between said speed control valve means and said flowcontrol valve means, and third fluid communication means between saidspeed control valve means and said speed control means of saidtransmission.
 1. A supply and control system for a hydrostatictransmission including; a source of fluid under pressure, flow controlvalve means for providing a constant volumetric rate of fluid flow,first fluid communication means between said source and said flowcontrol valve means, speed control valve means for regulating the flowof fluid from said constant volumetric rate of flow provided by saidflow control valve means to speed control means of said hydrostatictransmission, second fluid communication means between said speedcontrol valve means and said flow control valve means, and third fluidcommunication means between said speed control valve means and saidspeed control means of said transmission.
 2. The invention of claim 1wherein said flow control valve means include a first housing and a flowregulating first spool movably disposed within said first housing, saidspool having first and second chambers therein, said first chambercommunicating with said first fluid communication means and said secondchamber communicating with said second fluid communication means, firstorifice means in said first spool between said first and second chambersfor creating a drop in pressure of fluid flowing from said first chamberto said second chamber for causing movement of said first spool.
 3. Theinvention of claim 2 wherein said source includes a fluid supplyreservoir and a singular fluid pump.